1. Field of the Invention
The present invention refers to a method and a related apparatus for carrying out deep holes and/or bottle-boring, in particular in the field of high-precision machining, above all in the presence of a thin wall.
Such method and apparatus find specific application in boring, which consists in carrying out a longitudinal hole in a solid cylinder, to obtain a seamless tubular hollow cylinder. The so-called bottle-boring consists in a specific boring, in which the inside diameter (bore) of the longitudinal hole is greater than the diameter of the hole at the top of the cylinder, so that the hole has a shape resembling that of a bottle.
However, it is understood that the present invention may generally be applied to the carrying out of deep holes, where the ratio between final linear depth and hole diameter has a high value, e.g. higher than 10:1.
2. Description of the Prior Art
The boring is carried out by a tool covering a longitudinal distance with respect to the workpiece, supported by a tool shaft of appropriate length. The machining may be carried out on a lathe, where the workpiece to be bored is set in rotation with respect to the shaft or vice versa.
This kind of machining usually requires a high degree of accuracy, above all to ensure the perfect cylindricity and linearity of the hole that is carried out. Such a requirement is all the more difficult to meet the greater the depth of the hole, or the linear depth/hole diameter ratio.
Moreover, it should be considered that in several manufacturing processes even minimal deviations lead to the discarding of the workpiece, with a considerable economic loss in time, tool wear and often high-grade material.
In addition, difficulties are often enhanced by the end use of the hollow cylinders, envisaging the resistance to very high internal pressures and therefore requiring the use of specific metallic materials of difficult machining.
The carrying out of a bottle-boring further aggravates these overall difficulties.
All these difficulties prevented the carrying out of deep holes and borings with high depth/diameter ratios, e.g., higher than 14:1. In fact, with the increase of this parameter there increases the risk of tool shaft bendings and the transmission of vibrations therethrough.
To overcome this drawback, it has been proposed to make the shaft sturdier; yet, this contrivance, beside generally burdening the machining, may negatively influence the evacuation of the chips by the tool.